1. Field of the Invention
The present invention relates to a semiconductor device and the control method thereof.
2. Background Art
In recent years, the development of a semiconductor device called as an IPM (Intelligent Power Modules) has been proceeding which contains an IGBT (Insulated Gate Bipolar Transistors) and a driving circuit for driving the IGBT.
An IPM is a module for carrying out electric power conversion, which is widely used for applications such as an AC (Alternating current) servo, an air-conditioning device and an elevator.
As a related technology of an IPM, a technology is proposed by which an element for causing a time delay in a control voltage is disposed in the transmission path of the control voltage that drives an IGBT and, on the basis of the delayed control signal, a gate discharging transistor is made turned-off when the IGBT is turned-on and the gate discharging transistor is made turned-on when the IGBT is turned-off.
Moreover, a technology is proposed by which in making a semiconductor element turned-off, with a first MOSFET (Metal Oxide Semiconductor Field Effect Transistor) being made turned-off, a second and third MOSFETs with their respective on-state resistances different from each other are made turned-on.
In an IGBT with a fast switching speed, a voltage surge is produced at the turning-off thereof. A voltage surge with the maximum value thereof exceeding the maximum rated voltage of an IGBT might cause insulation breakdown. Therefore, it is important to suppress the increase in a voltage surge.
For turning-off an IGBT, the gate charges in the IGBT is to be extracted to lower the gate voltage. However, a strong gate charge extraction capability will result in a sudden increase in a voltage surge. Therefore, from the viewpoint of reducing the increase in a voltage surge, it is desirable to weaken a gate charge extraction capability.
However, a weak gate charge extraction capability causes difficulty in maintaining a gate voltage at a voltage sufficiently low for making an IGBT turned-off. Such a state is easily affected by noises, which causes a possible malfunction of turning-on the IGBT by a gate voltage increased by noises. Thus, from the viewpoint of inhibiting the malfunction of the IGBT, the gate charge extraction capability is to be made strong.
In this way, in a related IPM, there are problems in that strengthened gate charge extraction capability of turning-off an IGBT causes an increase in a voltage surge and gate charge extraction capability inversely weakened for avoiding an increase in such a voltage surge causes a malfunction of turning-on the IGBT that is to be turned-off. Therefore, a high performance IPM is desired for being provided in which the foregoing problems are solved for improved characteristics.
The invention was made by taking the foregoing points into consideration, and provides a semiconductor device in which an increase in a voltage surge is suppressed and a malfunction of the device is inhibited and the control method of the device.